Neuropathic pain, also referred to as a chronic pain, is a complex disorder resulting from injury to the nerve, spinal cord or brain. There is evidence that nerve fibers in subjects with neuropathic pain develop abnormal excitability, particularly hyper-excitability, Zimmerman (2001) Eur J Pharmacol 429 (1-3):23-37. Although the American Pain Society estimates that nearly 50 million Americans are totally or partially disabled by pain, there are currently very few effective, well-tolerated treatments available (Wetzel et al. (1997) Ann Pharmacother 31 (9):1082-3). Indeed, existing therapeutics cause a range of undesirable side effects primarily due to the difficulty in developing small-molecule drugs capable of specifically targeting the receptor/channel of choice.
Many, relatively common clinical conditions are associated with neuropathic pain (Berger A, et al. (2004) J Pain 5:143-149). Traditionally, combinations of tricyclic antidepressants or anti-epileptics along with analgesics have been used to treat neuropathic pain (reviewed in (Mendell J et al. (2003) N Engl J Med 348:1243-1255). However, treatment of neuropathic pain is often unsatisfactory; persistent neuropathic pain affects quality of life and lead to significant morbidity. In recent years with the identification of the receptor for capsaicin (Caterina M J et al. (1997) Nature 389:816-824; Caterina, M J et al. (2000) Science 288:306-313), neuropathic pain research has directed its attention to identification of drugs that interfere with the transient receptor potential vanilloid receptor 1 (TRPV1) physiology. Primary effort has focused on antagonists that block nociceptive pain sensation at the receptor level but so far, no drug has reached clinical use (Caterina M J et al. (1997) Nature 389:816-824 and Caterina, M J et al. (2000) Science 288:306-313)
Previous attempts at identifying TRPV1 antagonists have used non-neuronal cell lines expressing recombinant TRPV1 and the calcium flux induced by capsaicin as an outcome measure for high throughput screening (HTS) (Caterina M J et al. (1997) Nature 389:816-824; Caterina, M J et al. (2000) Science 288:306-313). Although these cells expressing recombinant TRPV1 may be useful, a nociceptive sensory neuronal cell expressing TRPV1 might be more relevant because the non-neuronal cell lines may lack the appropriate intracellular signaling pathways associated with and downstream of TRPV1 in nociceptive sensory neurons. In order to generate tools for a more rational approach to drug screening for neuropathic pain, it would be useful to have an immortalized DRG sensory neuronal line with nociceptive properties. To date, attempts to immortalize neuronal cell lines have achieved little success.
Likewise, the ability to generate immortalized cell lines using cells that have been historically difficult to immortalize would be beneficial in the efforts to develop novel therapeutics for the treatment of disease and illness.
Although neuronal cell lines have been generated in the past these were mostly from embryonic tissues and were derived from progenitor or stem cells (see, e.g., Bernard J (1989) Neurosci Res, 24:9-20, Evrard (1990) PNAS, 87:3062-6, Redies J (1991) Neurosci Res 30:601-15). Also, a temperature sensitive mutant T antigen has been used to immortalize neuronal populations, but the efficiency of this technique has been very low (Eves (1994) Brain Res 656:396-404).
Accordingly, the need exists for effective and reliable methods of immortalizing cells that scientists have not had success in immortalizing with currently available methods, e.g., neuronal cells.